From the Guidelines
Computed Tomography (CT) scans can be compared across different time points to monitor disease progression or treatment response, but the choice of imaging modality should be made considering factors such as sensitivity, specificity, radiation dose, and resource intensity, as highlighted in a 2021 study published in Radiology 1. When comparing CT scans, radiologists look for changes in size, density, or appearance of abnormalities such as tumors, infections, or inflammatory processes. For optimal comparison, subsequent scans should use similar protocols, including slice thickness, contrast administration, and patient positioning. The comparison process typically involves side-by-side evaluation of images, with measurements taken at identical anatomical locations. Modern radiology software often includes tools that facilitate direct comparison, such as subtraction techniques or overlay capabilities. Factors that may affect comparison accuracy include differences in breathing phase, contrast timing, or technical parameters between scans. CT comparison is particularly valuable in oncology for assessing tumor response to therapy using standardized criteria like RECIST (Response Evaluation Criteria in Solid Tumors), which provides objective measurements of target lesions. However, it's essential to consider the drawbacks of CT, including exposure to ionizing radiation and its associated risk of cancer, as noted in a 2010 study published in the European Heart Journal 1. This systematic approach to CT comparison helps clinicians make informed decisions about continuing or modifying treatment plans based on objective imaging evidence. Some key points to consider when choosing the specific imaging modality include:
- Compared to chest CT, chest radiography appears to have a lower sensitivity and might have higher specificity
- Chest CT has the highest sensitivity but relatively lower specificity and can be useful in patients with some pre-existing pulmonary diseases
- Lung ultrasound has very low-certainty evidence supporting its diagnostic accuracy but might be helpful with the appropriate expertise as a supplemental or alternative modality. Considering these factors and the potential risks associated with CT scans, the choice of imaging modality should be made through shared decision-making involving the referring physician, the radiologist, and the patient whenever possible, as recommended in the 2021 study published in Radiology 1.
From the Research
Comparison of CT Scans
- The use of CT scans has been a topic of discussion in the medical field, with some studies suggesting that they may increase the risk of cancer 2.
- However, other studies have found that the benefits of CT scans outweigh the risks, especially when used clinically warranted 3.
- In terms of comparison, a study found that low-dose non-enhanced CT and standard dose contrast-enhanced CT in combined PET/CT protocols for staging and therapy planning in non-small cell lung cancer had similar results in 47 out of 50 patients 4.
- Another study found that contrast-enhanced CT as part of the PET/CT protocol more accurately assessed the TNM stage in 8% of patients compared with non-contrast PET/CT 4.
- The influence of intravenous contrast medium and different contrast medium phases on attenuation correction, PET image quality, and clinical staging in combined PET/CT in patients with a suspicion of lung cancer was also evaluated, and it was found that contrast-enhanced CT is suitable for attenuation correction in combined PET/CT in lung cancer 5.
- A study comparing contrast-enhanced and nonenhanced helical CT of the thorax in patients with newly diagnosed lung cancer found that there was agreement in stage between the nonenhanced and contrast-enhanced examinations in 92 out of 96 patients 6.
Key Findings
- CT scans are a valuable diagnostic tool, but their use should be clinically warranted to minimize unnecessary exposure to radiation 3.
- The use of contrast-enhanced CT in PET/CT protocols can provide more accurate assessments of the TNM stage in some patients 4, 5.
- Non-enhanced CT and contrast-enhanced CT can have similar results in some cases, but contrast-enhanced CT can provide additional information in certain situations 4, 6.